The causes for 90% of childhood leukemias are unknown. Many studies suggest that environmental exposures of concern at Superfund sites, such as pesticides, metals, solvents, polychlorinated biphenyls (PCBs), and polyaromatic hydrocarbons (PAHs), may increase the risk of developing childhood leukemia. However, these associations are based on parental reports or occupational exposures. This proposal provides a special opportunity to extend an existing case-control study of childhood leukemia being conducted in the San Francisco Bay and Central Valley areas by directly measuring environmental and chemical exposures, evaluating the interaction of environmental exposures by directly measuring environmental and chemical exposures, evaluating the interaction of environmental exposures with genetic susceptibility, and increasing the sample size and duration of study enrollment. Approximately, 30-40% of the combined study population will be Hispanic. Currently, two of three tiers of an exposure assessment are being implemented. Tier 1 enrolls and interviews cases and controls seeking to identify risk factors for the disease, including residential and occupational chemical exposures. In Tier 2, cases and birth certificate controls that have not changed residence based on specific criteria (approximately 50% of the Tier 1 study population) are part of a reliability study, which seeks to determine if self reported chemicals used at the time of interview are found in the home during a visual survey several months after interview. The focus of the current proposal, Tier 3, aims to document the potential for household exposures by sampling dust on the floor surfaces in a subset of homes of cases and controls participating in Tier 2. The objective is to identify if there are differences in concentrations of pesticides, metals, polyaromatic hydrocarbons, cotinine, polychlorinated biphenyls, and ethylenethiourea in the homes of cases and controls. Further, a case-case analysis will identify if cases with chromosomal translocations of interest life in homes with higher concentrations of target compounds than cases that do not have such translocations. These analysis will determine whether leukemic children with common genetic changes experience common exposures and whether these genetic changes have approximately the same temporal occurrence. Further, we will evaluate whether children with and without leukemia differ with respect to susceptibility to leukemia.